ref: 970e4fcbaacb7511d45eaa2890501a0cc1edb45c
dir: lu9-p9/note.c
/*
* The following global state designates the Lua state
* responsible for registering and running note handler
* functions -- the one (and only) loading this module.
* Additionally the note itself is communicated to the
* postponed handler here due to most of Lua API not
* being safe to use in a note handler context.
*
* This global state and nondeterministic nature of
* postponed handling of notes means this module should
* be used with care and will likely need to be heavily
* adapted for use in any but the simplest of hosts.
* Lu9 standalone interpreter is an example of a simple
* program with a single Lua state and Lua code being
* "the boss", that is, the note is very likely to
* interrupt a Lua VM rather than host code, and if not
* the VM will be entered shortly after. This lets
* postponed note handlers run relatively close to
* the actual note event.
* In more involved programs, perhaps running multiple
* separate Lua states, or spending more time in the
* host, the postponed handlers may run only as soon
* as the designated handler state gets a chance to
* run, if at all.
*
* In short, consider alternatives to Lua code doing
* any direct note handling.
*
* TODO: the note state, catcher and exit functions,
* and notify registration should all be left for the
* host to set up.
*/
typedef struct Note Note;
struct Note {
lua_State *L;
char note[ERRMAX+1];
};
static Note notestate;
/*
* Acks the note so it can be handled outside note context
* but only after the possibly interrupted Lua state
* stabilizes. This is done by registering an instruction
* hook and running handler functions inside it.
* Note that another note may come just as we are doing
* this. We do nothing about it currently: the newer
* notes simply interrupt currently executing handlers.
* One solution is to queue incoming notes and handle
* all of them in order.
* Also note that this catcher always acknowledges the
* note, preventing any other catchers registered after
* it from ever seeing the note. Therefore you most
* likely want it to be the last or only note handler.
*/
static int
notecatcher(void*, char *note)
{
static void noterunner(lua_State*, lua_Debug*);
lua_sethook(notestate.L, noterunner,
LUA_MASKCALL|LUA_MASKRET|LUA_MASKCOUNT, 1);
strncpy(notestate.note, note, ERRMAX);
return 1;
}
static void
noterunner(lua_State *L, lua_Debug*)
{
int n, i;
lua_sethook(notestate.L, nil, 0, 0);
if(lua_getfield(L, LUA_REGISTRYINDEX, "p9-note-handlers") != LUA_TTABLE)
luaL_error(L, "missing note handlers table");
if((n = lua_rawlen(L, -1)) == 0)
return;
for(i = 1; i <= n; i++){
lua_rawgeti(L, -1, i); /* handler(note) */
lua_pushstring(L, notestate.note);
if(lua_pcall(L, 1, 1, 0) != LUA_OK)
break;
if(lua_toboolean(L, -1) == 1)
return; /* to where we got interrupted */
lua_pop(L, 1);
}
/* Emulate kernel handling of unacknowledged note. */
if(strncmp(notestate.note, "sys:", 4) == 0)
abort();
exits(notestate.note); /* threadexitsall when using thread.h */
}
static int
noteset(lua_State *L)
{
if(lua_getfield(L, LUA_REGISTRYINDEX, "p9-note-handlers") != LUA_TTABLE)
return luaL_error(L, "missing note handlers table");
lua_insert(L, -2);
lua_rawseti(L, -2, lua_rawlen(L, -2) + 1);
lua_pop(L, 1);
return 0;
}
static int
noteunset(lua_State *L)
{
int n, pos, fn, t;
fn = lua_gettop(L);
if(lua_getfield(L, LUA_REGISTRYINDEX, "p9-note-handlers") != LUA_TTABLE)
return luaL_error(L, "missing note handlers table");
t = fn + 1;
n = lua_rawlen(L, t);
for(pos = 1; pos <= n; pos++){
lua_rawgeti(L, t, pos);
if(lua_rawequal(L, fn, -1))
goto remove;
lua_pop(L, 1);
}
lua_pop(L, 2);
return 0;
remove:
lua_pop(L, 1);
for ( ; pos < n; pos++) {
lua_rawgeti(L, t, pos + 1);
lua_rawseti(L, t, pos);
}
lua_pushnil(L);
lua_rawseti(L, t, pos);
lua_pop(L, 2);
return 0;
}
static int
p9_note_catch(lua_State *L)
{
int fn;
const char *arg;
fn = lua_gettop(L);
luaL_argexpected(L, fn > 0, 1, "function expected");
if(fn == 1)
arg = "set";
else
arg = luaL_checkstring(L, 1);
luaL_argexpected(L,
lua_type(L, fn) == LUA_TFUNCTION, fn, "function");
if(strcmp(arg, "set") == 0)
return noteset(L);
else if(strcmp(arg, "unset") == 0)
return noteunset(L);
return luaL_error(L, "'set' or 'unset' expected");
}
static int
p9_note_post(lua_State *L)
{
int pid, w;
const char *who, *note;
who = luaL_checkstring(L, 1);
if(strcmp(who, "proc") == 0)
w = PNPROC;
else if(strcmp(who, "group") == 0)
w = PNGROUP;
else
return luaL_argerror(L, 1, "expected 'proc' or 'group'");
pid = luaL_checkinteger(L, 2);
note = luaL_checkstring(L, 3);
if(postnote(w, pid, note) == -1)
return error(L, "postnote: %r");
lua_pushboolean(L, 1);
return 1;
}
static luaL_Reg p9_note_funcs[] = {
{"post", p9_note_post},
{"catch", p9_note_catch},
{nil, nil},
};
int
luaopen_p9_note(lua_State *L)
{
/* Only one Lua state may work with notes */
if(notestate.L != nil)
return 0;
notestate.L = L;
lua_createtable(L, 1, 0);
lua_setfield(L, LUA_REGISTRYINDEX, "p9-note-handlers");
luaL_newlib(L, p9_note_funcs);
atnotify(notecatcher, 1);
return 1;
}